Processes for the synthesis of glycerol carbonate are widely described in the literature.
Processes employing organic carbonates have been developed.
EP 0 739 888 discloses in particular a process for the preparation of glycerol carbonate by reaction of glycerol and a cyclic organic carbonate in the presence of a solid catalyst comprising a bicarbonate-comprising or hydroxyl-comprising anionic macroporous resin or a three-dimensional zeolite of X or Y type comprising basic sites, at a temperature of between 50 and 110° C. The reaction yield is of the order of 90%. However, in order to obtain this yield, it is necessary to withdraw the ethylene glycol formed during the reaction. The process is applicable to pure glycerol and to glycerins.
It is also known from US2010/0209979 (Jung et al.) a process for the preparation of glycerol carbonate by reaction between dimethyl carbonate and glycerol by transesterification catalyzed by a lipase.
JP06329663 discloses a process for the preparation of glycerol carbonate by reaction between ethylene carbonate and glycerol catalyzed by aluminum, magnesium, zinc, titanium or lead oxides. Other processes have been developed by catalysis with CaO.
However, these catalysts are not stable and are in particular decomposed by water and do not make it possible to be able to carry out the process continuously.
There are other processes using in particular phosgene and urea. However, the process with phosgene exhibits the disadvantage of being highly toxic and thus not suitable for the preparation of products involved in the manufacture of food, cosmetic or pharmaceutical compositions.
Thus, EP 0 955 298 discloses a process for the synthesis of glycerol carbonate consisting of the reaction of glycerol with urea in the presence of a catalyst of metal or organometallic salt type exhibiting Lewis acid sites. The molar yield obtained is between 40 and 80% with respect to the glycerol.
However, the processes with urea generate a high proportion of ammonia; it is thus necessary to neutralize this ammonia in the salt form and these ammonia salts are not of economic value. Disadvantages in terms of cost, of difficulty in purification and sometimes of environmental (in particular discharge of dioxane and/or glycidol, use of glycidol, use of tin-based catalyst, use of acetonitrile) are also described.
The catalysts of the prior state of the art generally comprise a basic entity, in particular of metal oxide type. This basic entity is soluble in the presence of water or hydratable (undergoes a reaction with water), which damages its effectiveness. It is thus important to control the reaction medium, in particular the amount of water, in order to employ such catalysts.
There is thus a need to provide a process which can be easily operated industrially, which can be employed continuously and which does not exhibit a risk, in particular in terms of toxicity. There is also a need to provide a process which can be carried out in a reaction medium comprising water.